docs: update README, dev scripts, and documentation

Update project documentation and development scripts.

- Update README test counts (953/957 passing, 8 skipped)
- Simplify dev script: remove test DB seeding, add name history creation,
  clean up stale test databases on startup, remove -p 1 test flag
- Update obsidian documentation for new features:
  - Name history system docs
  - Referral discount system docs
  - Database migration docs (CHAR(12) short IDs)

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

README.md

@@ -74,7 +74,7 @@ Default logins (password: `password`):
 ```bash
 cd backend && go build -o bin/backend ./main.go
 cd frontend && npm ci && npm run build
-cd backend && go test -tags "test,dev" -p 1 ./...   # 803/806 passing, 3 skipped
+cd backend && go test -tags "test,dev" ./...   # 953/957 passing, 8 skipped
 ```
 
 ## Full Documentation